Stabilization of rubber materials with cresylic acid derivatives



Patented July 29, 1952 STABILIZATION OF RUBBER MATERIALS WITH CRESYLICACID DERIVATIVES Leland J. Kitchen, Akron, Ohio, assignor to TheFirestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio NoDrawing. Original application July 1, i94sj, Serial No. 36,298.Divided'and this application July 28, 1951, Serial No. 239,179

8 Claims. (ill. 260 i5.95)

This invention relates to the stabilization of rubbery materialsbyincorporating therein reaction products of an alkyl halide and anolefinalkylated cresylic acid.

In the refining of petroleum there is obtained a product known asthe'cresylic acid fraction, which is composed chiefly of mixed cresols,xylenols, and other alkylated phenols Whose alkyl groups comprise atotal if no more than about three carbon atoms. One such commercialproduct has a boiling range of 92 to 121 C. at a pressure of 10millimeters of mercury. This boiling range is generally typical of suchproducts. Alkylation with an olefin yields a product which has value asa stabilizer in natural and synthetic rubbers. The olefin used maycontain about three to about eight carbon atoms-e. g., isobutylene,amylene, propylene, the octenes, etc.and a mixture of these may be used.A catalyst, such as sulfuric acid, facilitates the reaction. The productcontains a mixture of alkylated compounds, some of which are more highlyalkylated than others. I

A more highly alkylatecl, phenol-that is, a product which, on theaverage, contains more alkyl substituents-has greater inhibiting value.However, it is impossible to increase the alkylation by the cheapoleflns available-i. e., those containing about three to about eightcarbon atomsbecause the alkylation process is reversiblaand maximumalkylation is obtained when equilibrium conditions are reached.Commercially, the product of the alkylation may be distilled to separatea higher boiling fraction, and the remaining lower boiling fractionmaybe recycled with, fresh cresylic acid and again subjected toalkylation.

It has now been found that the product of such alkylation can be furtheralkylated by treatment with an alkyl halide in the presence of acatalyst which is the halide of a low molecular weight metal of thethird group of the periodic system; e. g., aluminum bromide, aluminumchloride,

boron chloride, boron fluoride. The alkyl halide as wellgas aftervulcanizing. They are substantiallynon-discoloring and are .useful inlightcolored stocks, such as those tobe used for whites sidewall tires,etc. l Although the use-of the stabilizer in synthetic rubbers will beexemplifiedherein by formula tions in butadiene copolymers of styreneand acrylonitrile, it may be used generally in rubberlike polymerizatesof 1,3-butadiene or other hydrocarbon conjugated dienes', such as forexample, isoprene, pentadiene, piperylene, dimethylbutadien'eand-2-methylpentadiene. For instance it may be used in rubber-like'copolymers of a conjugated diene and a vinyl aromatic compound, suchas, for example, styrene, alpha-methylstyrene, nuclearly substitutedstyrenes, mono chlorostyrene;dichlorostyrene, vinylnaphthalene,vinylbiphenyl; vinylcarbazole, 2-vinyl-5-ethylpyridine;Z-ethyl-S-vinylpyridine, commercially exemplified by CiR-S. It maybeused in rubber,- like copolymers of 'aconjugated diene andfa,monomerhaving the formula CHz- -C(R)--CX when R. is chlorine, methyl,ethyl, propyl or hy-i drogen and X is --CN, -CONH2, COR' or -COOR and Ris an alkyl group which contains one to five carbon atoms; a commercialrubber of this type is GR-A. It may also be used in the stabilization ofhomopolymers of '1,3-butadiene, isoprene,'etc.

The following table gives the boiling range of a cresylic acid fraction,and for comparison the boiling range of the products resulting from (a)alkylation by an olefin, (b) alkylation by an alkyl halide, and (c)alkylation by an olefin followed by alkylation by an alkyl halide. Thetable includes the'per cent of residue obtained and an indication oftheviscosity of the various products.

TABLE 1 The table shows that the product of, the two-step alkylation isa higher boiling, more viscous prodg uct. It was ;prepared as follows:

One hundred grams of a petroleum cresylic acid 3 cut of boiling-pointrange 92-121 C./ millimeters and containing 50 grams of toluene asdiluent and grams of concentrated sulfuric acid catalyst were stirred at70 C. for 3 hours while a stre'am: ofisobutylene gas was passed throughit. The mixture was washed and distilled, yielding a l2'7-gram fractionof a light yellow distillate with a boiling range of 101-157 13/10millimeters.

JIwenty grams of anhydrous aluminum chloride were dissolved in 100 gramsof the above tertbutylated cresylic acid fraction. The mixture wasstirred at 38-45 C. for 8 hours during which 200 grams of tert-butylchloride were added slowly. The reaction mixture was washed with waterand with sodium carbonate solution, and was then distilled. The productof this further alkylation step was a dark red, viscous liquid of"boiling point 100-220 C./ 10 millimeters. About 10-gramsof residueremained in-"the'still pot; The 'redproduct was used: as the" teststabilizer injt he work reported below.

I .Two per cent .of thisreaction' product. as a sojdiuinjoleate aqueous,emulsion, wasmixed. with a.GR,' S.latex obtained by emulsioncopolymerization- .of. l,3-butadi'ene and styrene. Two percent ofa..commercial stabilizer herein identified as stabilizes-No. 1.:(heptylated diphenylamine) was similarly compounded. with :thelatex;Coagula obtained ribygeoagulationwithaluminum sulfate were dried andthen; wereccmpounded in the followingzformulaz Partsco'polymereiestabilizer 100.0 coumaro'neresinh' 10.0 Accelerator 1.1Magnesiumo d 810 Wax ",1. 2.0 Zine oxide- .100'.0 Ultramarine .blueri,..7. 0.1

flitanium dioxide; 30.0 4.0

Sulfur.

The stocks,-- cured'for50 minutes at---300 0., on testingwere foundtohave the following properties, before and after aging four days-at 212? E.

. TAB E2.; -PHYsIeAL1rRoPERTIEs.or!

GRF-SLVULCANIZATE.

-Two-step, Stabilizer Reaction Product Unaged Vulcanizate:

Stress at 300% elongation (p. s. i) 400 400 Tensile strength (p. s. i.)925 775 Percent elongation at break 435. 390 Aged Vulcanize te:

Stress at 300% elongation (p.- 900 Tensile strength (p.:s. i.) 900; 625Percent elongation at break 300 260 (p. s. i. stands ior..pounds persquare inch'.).

The same stocks andanstock similarly compounded with coagulum containingtwoper' cent of another commercial stabilizer identified'herein asstabilizer No. 2 (an alkylphenol sulfide) were subjected to. a.weatheringtest. Tapered strips elongated 12 /2 -percent. were exposed tothe weather for-fourmonths. with--the followingresults:

TABLE 3.GR,S VULCANIZATE WEATHER TESTS Color Checking Stabilizer FrontBack Front Back Two-Step Reec- No change No change. Slight None.

tionproduct. Stebi1izer.No.1 .Tan Tan Severe... Do. StabiIizer1No.2. Nochange Veryslightdis- Moderate. Do.

' coloration.

Thus the copolymer stabilized with the reaction product of the two-stepalkylation was superior toth'at similarly stabilized with the commercialstabilizers.

The same'vulcanized stocks were subjected to artificial light and theresults of the exposure are recorded in the following table:

TABLE: 4..-LIGHT TESTS ON1GR=S VUL- 'CANIZATE A. Exposure in jadeometer01'- 1'0"hours ati12 5-- F.

S tabilizer Color:

Reaction Product Bleached. StabilizerNo. 1 Medium browns. Bleached.

Stabilizer. No. 2

B. Eftposure'to: sun lamp: 16 hoursrat'i7 molten.

Stabiliier Color- 4 Reaction Product Stabilizer N o; 1 Stabilizer N0. 2

an. Light cream,

The stock'containing the stabilizer of this invention gave substantiallyno discoloration?- Tests were conducted on rubber-like copolymer i ofbutadiene and acrylonitrile; referred to herein -as GRT-A: The stockswere prepar'ed by O 1 M After Aging c or eore Stabilizer Aging.

Color Condition Tgoste iieamon Pro- Tan Light brown" Exce1lent. uc IStabilizer No.3 Brown Darkbrown;;; Do;

Blank Light tan... Dirty brown Poor..

The-sample'which contained no stabilizer deteriorated and hardened onaging. The reaction product of the "two-steplalky1ationprovidedhageresistance without as much discoloration: as: the commercial stabilizer.

Stocks were compounded accordingto the, following formula: j

' P t Copolymer, with or without stabilizer 100.0

The vulcanizates were subjected to oven-aging and air-bomb aging.oveneaging involved heating four days at212 F; Air-bomb aginginvolvedheating under 60 pounds air pressure for 15-h0urs at 260? F. Thefollowing. table lists'the physical properties of the differentproducts:

TABLE 6.-'--PROPERTIES OF CURED GR-A Two-Step Stabi- Reaction lizerBlank Product No. 3

Unaged Vulcanizate:

Stress at 300% elongation (D. S. i. l, 525 l, 475 2.600 Tensile strength(p. s. i.) 4, 425 4. 475 3, 212 Per cent elongation at break.... 580 590335 Oven-aged Vulcanizate:

Stress at 300% elongation (p. s. i.) 3, 550 3, 475 Tensile strength (p.s. i.) 3, 950 435 2, 025 Per cent elongation at break. 330 365 250Air-bomb-aged Vulcanizate:

Stress at 300% elongation p. s. Tensile strength (p. s. i.) 3, 100 3,475 2, 300 Per cent elongation at break. 270 290 100 Thus the stockcontaining the reaction product of the two-step alkylation product wasfar superior in age resistance to vulcanizate containing no stabilizer.It compared favorably with that containing the commercial stabilizer.The following table shows that it is substantially non-discoloring.

The GR-A stocks and a GRr"A stock similarly compounded, butcontaining'the aforesaid stabilizer No. 1 were compounded in a mix whichwas heavily loaded with white pigment, as follows:

Parts Copolymer with or without stabilizer 100.0 Coumarone resin 7.5Sulfur 1.0 Magnesium oxide 5.0 Zinc oxide 85.0 Neutral clay 20.0Titanium dioxide 20.0 Accelerator 1.3

The stocks were cured sixty minutes at 280 F. The vulcanizates wereexposed to artificial weathering by exposure in a fadeometer for tenhours at 125 for sixteen hours at seven inches. are recorded below.

TABLE '7.LIGHT TESTS ON CURED GR-A The results Color after Color afterStabilizer fadeometer sun lamp exposure exposure Reaction Product Lightcream" Light cream. Stabilizer No. 1. Light tan Light tan. StabilizerNo. 3. Brown Gray brown. Blank Light cream... Light cream.

Both commercial stabilizers caused discoloration, whereas the stabilizerof this invention was substantially non-discoloring. It discolored nomore than the stock containing no stabilizer.

F. and exposure to a sun lamp 6 It was also shown t'o be substantiallynon-discoloring byexpo'sure to natural sunlight.

The reaction product of the two-step alkyla, tion was also ioundtoinhibit 'the fiex-cracking of natural rubber; A stock compoundedaccording to thefollowing formula and'a stock similarly compounded butcontaining nostabilizer was cured sixty minutes at 280 F.

stocks remained white. Neither did discoloration appear on, artificialweathering in a weatherometer.

one half inch tapered; strips; of the two natural rubber stocks wereflexedlwith 0-75% elongation until'all strips 'were'broken. Cracks inthe :broken strips were counted. The stocks 1 were evaluated accordingto flex life and rate of crack formation. The figures in thefollowingtable are averages for a number of strips.

TABLE 8.NATURAL RUBBER FLEXING The stabilizer of this invention providedconsiderable improvement in the flex life of this natural rubberwhite-sidewall stock.

The amount of stabilizer used may vary. Ordinarily about 0.1 to 10.0parts on the rubber will be used. It may be mixed with otherstabilizers. The examples are only illustrative of the invention and allparts given therein are by weight.

This application is a division..-of applicant's application No. 36,298filed July'l, 1948, and now abandoned.

What is claimed is: i

1. Process of stabilizing a vulcanized rubber composition withoutsubstantially increasing its susceptibility to discoloration in light,which comprises adding to an unvulcanized rubber a relatively smallamount of the reaction product of an alkyl halide and anolefin-alkylated cresylic acid the alkyl halide containing 3 to 8 carbonatoms in the molecule and the olefin containing 3 to 8 carbon atoms inthe molecule, and then vulcanizing the rubber.

2. A vulcanized rubber composition containing a relatively small amountof the reaction product of an alkyl halide and an olefin-alkylatedcresylic acid the alkyl halide containing 3 to 8 carbon atoms in themolecule and the olefin containing 3 to 8 carbon atoms in the molecule,the composition characterized by its stability when subjected tooxidative conditions.

3. Process of stabilizing a rubber composition without substantiallyincreasing its susceptibility to discoloration in light, which comprisesincorporating in an unvulcanized rubber a rela- 7 tively small amount ofthe-reaction product of an alkyl halide and an olefinalk'ylatd cresylicacid the alkyl halide containing} 3 to- 8 Carbon atomsinthe molecule andthe-olefin containing 3:. toll8 c'arbon atoms-in the molecule;

4 A stabilized .lrubbern composition containing a relatively smallamount of thereaction .product of an alkyl halide and-U an"olefinealkylated cresylic acid the alk'yl'halide containing 3 to 8carbon atoms'in. the molecule. and the olefin containing 3 to 8 carbonatoms in the molecule, the composition characterized by its stabilitywhen subjected to oxidative conditions and further characterized by itsresistance to discolorae tion when exposed tdlight.

5. Process'of stabilizing a rubber latex against deterioration due tooxidation and .heatcornprising incorporating in the latex a relativelysmall amount of the reaction product of an alkyl halide and anolefin-alkylated cresylic acid the alkyl-halide containing 3' to 0carbon atoms per molecule and the olefin containing 3 to 8 carbon atomsper molecule.

6. A rubber latex-comprising arelatively small amount ofthe reactionproduct of an 'alkyl halide and an olefin-alkylated cresylic acid thealkyl halide containing 3 to 8 carbon" atoms per molecule and the-olefincontaining 3--to8 carbon atoms per molecule, the latex and the rubberNumber thereof: characterized .by 'superior resistance towarddeterioration due to oxidation and, heat and by resistance todiscoloration when exposed tollight.

7. A stabilized rubber composition containing a relatively small amountof the reaction product of: tertiary butyl chloride and isobutylene:alk-ylated petroleum cresylic acid, the, reaction product being aviscous liquid boiling at substantially 100-220" C. at 10 mm.

8. Process of stabilizing a rubber against .deterioration during. dryingof the rubber, comprising incorporating in a rubber latex a T818:tively'small amount of the reaction productof an alkyl halide and anolefin-alkylated cresylic acid the alkyl halide containing 3 to' 8carbon atoms pertmolecule and the olefin containing 3 to 8 carbon atoms:per molecule, co-coagulating the latex and reaction'product, and thendrying the resulting coagulum.

LELAND J. KITCHEN.

REFERENCES'CITED The following references are'of recordin'the file ofthis patent: V

UNITED STATES PATENTS Name Date 7 2,471,887 n lson V May 31,1949

1. PROCESS OF STABILIZING A VULCANIZED RUBBER COMPOSITION WITHOUTSUBSTANTIALLY INCREASING ITS SUSCEPTIBILITY TO DISCOLORATION IN LIGHT,WHICH COMPRISES ADDING TO AN UNVULCANIZED RUBBER A RELATIVELY SMALLAMOUNT OF THE REACTION PRODUCT OF AN ALKYL HALIDE AND ANOLEFIN-ALKYLATED CRESYLIC ACID THE ALKYL HALIDE CONTAINING 3 TO 8 CARBONATOMS IN THE MOLECULE AND THE OLEFIN CONTAINING 3 TO 8 CARBON ATOMS INTHE MOLECULE, AND THEN VULCANIZING THE RUBBER.